Multiband radio receiver



Feb. 6, 1940. V E, THQMAS 2,189,688

MULTIBAND RADIO RECEIVER Filed Jail. 5, 1938 MEANS r-i a, A :4 zw l c 5 d Q p c 72 flunwnr/c Van/ms 4 I v 00/77/204 are Gram 5/,45 SUPPLY Patented Feb. 6, i 940 UNITED STATES MULTIBAND RADIO RECEIVER Harry E. Thomas, Philadelphia, Pa., assignor to Phileo Radio and Television Corporation, Philadelphia, Pa., a corporation of Delaware Application January 5, 1938, SerialNo. 183,555

In Great Britain January 25, 1937 6 Claims. (Cl. 250- 20) This invention relates to improvements in multibandradio receivers which are adapted to receive signals in a plurality of frequency bands.

More particularly, the invention relates to novel means for suppressing or attenuating undesired signals in radio receiving systems of this type. By means of the invention, it is possible to attenuate the so-called image signals in radio receivers of the superheterodyne-type, and it is also possible to attenuate certain other undesired signals having a frequency inthe neighborhood of the intermediate frequency ofthe receiver. The present invention is in the nature of an improvement over that disclosedand claimed in copend- I ing application Serial No. 183,542 filed January 5, 1938. I v

The principal object ofthe invention isto provide a novel device of this character which may be employed to'advantage in a superheterodyne multiband receiver, that is a receiver adapted bands, and which device embodies a minimum number of circuit elements and utilizes certain elements in a dual manner.

Another object of the invention is to provide a multiband receiver of the superheterodyne type in which the coil or coils of an unused wave band are employed to attenuate undesired intermediate frequency or image signals associated with the desired signals in the particular wave band being used, and in which the same'coils are used for the transfer of desired signals in their particular wave bands, thus permitting the coils to serve a dual purpose.

Although the principles of the invention are applicable in any instance where it is desired to attenuate undesired signals and to transfer desired signals substantially unaffected, as stated above, the invention is particularly adapted for use in a superheterodyne multiband radio receiver and, therefore, it will be described herein with particular reference to such specific application.

As is now well known, any superheterodyne receiver is responsive to signals of two difierent frequencies which represent the sum and difference, respectively, of the oscillator frequency and the intermediate frequency of the receiver. To a lesser extent, the receiver is also responsive to signals whose frequencies represent the sum and quency and harmonics of the oscillator frequency. One of the signals to which the receiver is responsive is commonly known as the image signal. The presence of the image signal is particularly difference, respectively, of the intermediate freundesirable in certain instances, for example in the reception of signals in .the long wave band, that is, signals having a frequency in the frequency range between 150 and 350 kilocycles, since the image signals corresponding thereto lie in the standard broadcast band which extends from 550 Pilocycles to 1600 kilocycles within which there are present signals emanating from powerful transmitting stations. For example, if the I intermediate frequency of a receiver is 450 kilo- 1,

cycles, the image frequency range corresponding to signals in the long Wave band will extend from '750'kilocyc1es to 1250 kilocycles. Therefore, in order to receive signals in the long Wave band efficiently, it is necessary that the strong image ll signals present in the broadcast band be effective- 1y attenuated.

In the reception of signals in the broadcast band, the suppression of imagesignals is relatively unimportant, but it is desirable to attenuate or suppress signals having frequencies in the neighborhood of the intermediate frequency of the receiver, which signals combine with the intermediatev frequencysignal to produce whistles or other undesirable noise signals.

The present invention provides novel means for effectively attenuating boththe undesired image signals and the signals having frequencies in the neighborhood of the intermediate frequency, employing the wave band coils of the receiver forv these purposes in the manner described hereinafterp I i Other objects and features of the invention will be apparent from consideration of the drawing and specification.

In the drawing:

Fig. 1 is illustrative of one form of the invention. I

Fig. 2 is. an illustrative diagram showing in schematic form the coils which may be employed 0 in the circuit of Fig. 1. v

Referring now to Fig. 1 of the drawing, there is shown a multiband receiver which is adapted to receive signals in the long-wave band and the broadcast band as abovementioned. For this 4,5

nected to the input element of the tube V and when the switch S is thrown to the position 2, the coil BC is connected to the input element. The coils LW and BC are inductively coupled as indicated by M in the illustration.

Signals may be supplied to the several tuned circuits from a conventional high impedance antenna A through the resistance-capacitance coupling network R1C1C2. The tube V may be a conventional detector oscillator or it may be a conventional tube of the mixer type. In any case, there will be associated with the tube V an oscillator having a tuning condenser Cu, which condenser may be ganged with the tuning condenser Ct for simultaneous operation of the two tuning condensers, as indicated by the brokenline representation. Suitable grid bias or automatic volume control bias may be supplied to the grid of tube V by means of the isolating resistance R2 and filter condenser C4. The output of the tube may be supplied to suitable utilization means such as the intermediate frequency amplifier of a conventional superheterodyne radio receiver.

Following the practice of the invention, there is provided a second switch S2 which is preferably arranged for simultaneous operation with the switch S1, as indicated, and which is adapted to connect the coil BC to the condenser Cs when thrown to the position I corresponding to the position i of the switch S1. Suppose that it is desired to receive signals in the long-wave band, in whiclzi case the switches S1 and S2 will be thrown to their corresponding positions I. The coil LW will then be connected to the input element of the tube V and the coil BC will be conncctcd to the condenser C3. The coil BC and condenser C3 thus form a series circuit which is coupled to the tuned circuit LWCt by the mutual inductance M. When made resonant at the 4 lower end of the image signal band correspondcated may be 450 kilocycles.

ing to the lower part of the long-wave band, this circuit will attenuate image signals in the image signal band corresponding to the long-wave band. More specifically, this series circuit maybe made resonant at a frequency of about 750 kilocycles at the lower end of the image signal band.

When it is desired to receive signals in the broadcast band, the switches S1 and S2 will be thrown to their corresponding positions 2, thus i connecting the coil BC to the input element of the tube V. The coil LW and its associated padding condenser Cpl are made resonant at a frequency in the neighborhood of the intermediate frequency of the receiver, which as above indi- These elements then form a trap circuit which is inductively associated with the coil BC and which serves to suppress or attenuate signals having frequencies in the neighborhood of the intermediate frequency.

Thus, it will be seen that during the reception signals in the long-wave band, the coil BC is cinpioyed in the suppression of image signals, while during the reception of signals in the broadcast band, the coil LW is employed in the suppression of signals approximating the intermediate frequency.

In this manner, these two types of undesired signals are attenuated or suppressed employing the coils i W and BC for dual purposes.

I adjusting the padding condensers of the re- 0 for the purposes in view, the following proe is followed: The receiver is first adjusted for reception of signals in the broadcast band and the padding condenser CpZ is then adjusted.

Following this adjustment, the switches S1 and S2 are adjusted to receive signals in the longwave band and the padding condenser Cm is adjusted, allowing the adjustment of the padding condenser C z to remain as previously adjusted. The adjustment of the padding condenser Cpl determines the resonant frequency of the trap circuit formed by this condenser and the coil LW. By proper design of the coils LW and BC with respect to the tuning condenser Ct, the adjusted value of Cpl may be arranged to be the proper value to tune coil LW to approximately the intermediate frequency thus eliminating the need of a further padding operation, or the use of an additional padding condenser.

The coils LW and BC should preferably be wound as illustrated in Fig. 2. It will be noted that these coils are wound on a common form F adjacent one another and in the same direction as illustrated.

In a typical example, the various elements of the system had the following characteristics. The coil LW comprised 400 turns of 340 Litzendraht wire and the coil BC comprised 97 turns of 7--41 Litzendraht wire, both coils being universally wound on a one-half inch form of core. The inductance of coil LW was 3079 microhenries, while the inductance of coil BC was 284 microhenries. The mutual inductance between the two coils was 109.7 microhenries, which was obtained by spacing the coils about a half an inch apart.

The padding condenser C 1 had a capacitance of about 60 micro-microfarads, while the padding condenser C z had a capacitance of about 10 micro-microfarads. It will be understood that these values will vary considerably with different coils. The tuning condenser Ct had a capacitance range of 30 to 370 micro-microfarads.

The impedance of resistor R1 was 10,000 ohms The capacitance of condenser C1 was 6,000 micromicrofarads. That of condenser C2 was 2,250 micro-microfarads, and that of condenser C3 was 250 micro-miorofarads.

Although the invention has been described with particular reference to a specific form or embodiment, it will be understood that it is not thus limited but is capable of various changes and modifications without departing from its scope.

I claim:

1. In a superheterodyne radio receiver. a signal channel, a source of signals, a plurality of tuning coils, there being some mutual coupling between said coils, a single means for tuning the coils to different frequencies in different wave bands, means including a switch for connecting difierent ones of said coils in the signal channel to transmit the desired signals in the different wave bands, and means including a padding condenser permanently connected in shunt with one of said coils for preventing the transfer of undesired signals associated with the desired signal being transmitted by another of said coils.

2. In a multiband superheterodyne radio receiver, a source of signals, a timing condenser, a plurality of coils, each of said coils being tunable by said tuning condenser to transfer desired signals in different wave bands, there being some mutual coupling between said coils, a common connection between one end of each of said coils, connections for transferring signals from said source to said common connection, an amplifier, having an input circuit means connecting the tuning condenser in shunt with the input circuit for said amplifier, a Wave band switch for alternatively connecting the other ends of said coils to path being constructed and arranged to suppress the tuning condenser to transfer desired signals in the respective wave bands, and a padding condenser permanently connected in shunt with one of said coils, said coil and said padding condenser being constructed and arranged to suppress undesired signals associated with the desired signals transferred by said other coil.

3. In a multiband superheterodyne radio re-,

ceiver, a signal channel, a tuning condenser, a coil tunable to a desired signal in one wave band by saidcondenser, a second coil tunable to a desired signal in a difierent wave band by said condenser,

the coils being mutually inductively coupled, a wave band switch for connecting one coil in the signal channel for transferring desired signals in its wave band and for alternatively connecting the second coil in the signal channel for the transfer of desired signals in the second wave band,,

means for utilizing said second coil to prevent the transfer of undesired signals when said first coil is transferring desired signals, and means for utilizing said first coil to prevent the transfer of undesired signals when said second coil is transferring desired signals.

4. In a multiband superheterodyne radio re- ,reiver, a source of signals, a tuning condenser, a

plurality of coils, each of said coils being tunable by said tuning condenserto transfer desired sig-'- nals in different wave bands, there being some mutual coupling between said coils, a common connection between one end of each of said coils, connections for transferring signals from said source to said common connection, an amplifier having an input circuit, means connecting the tuning condenser in shunt with the input'circuit of said amplifier, a wave band switch for alternatively connecting the other ends of said coils to the tuning condenser to transfer desired signals in.

the respective wave bands, switch means-for connecting one of said coils in series with a condenser .to form a shunt path across said signal source when the other of said coils is connected to transfer desired signals, said one coil and said shunt undesired signals associated with the desired signals transferred bysaid other cell, and a padding condenser permanently connected in shunt with said other coil, said other coil and said padding condenser being constructed and arranged to sup-- press undesired'signals associated with the desired signals transferred by said one coil.

5. In a multiband receiver, a source of signals, signal transfer means, a tuning condenser connected across said transfer means, a connection,-

between one sideof said source and one side of said transfer means, a plurality of mutually coupled coils, a common connection between one end of each of'said coils, means connecting the other side of said source to said common connection,

switching means for selectively connecting the other ends of said coils to the other side of said transfer means, the said coils being tunable respectively by said condenserover different frequency bands, and means including a padding condenser permanently connected in shunt with one of said coils for preventing the transfer of undesired signals during the transfer of desired signals by another of said coils.

'6. In a multiband receiver, a source of signals, signal transfer means, a tuning condenser connected across said transfer means, a connection between one side of said source and one side of i said transfer means, a plurality of mutually coupled coils, a common connection between one 1 end of each. of said coils, means connecting the other side of said source tosaid common connection, switching means for selectively connecting the other ends of said coils to the other side of said transfer means, the said coils being tunable respectively by said condenser over different frequency bands, means for utilizing'one of said 

